It is known that N-substituted-6-pyridine carboxamide or thiocarboxamide has a herbicidal activity, as described, for example, in Japanese Patent Application Laid-open (KOKAI) No. 4-290805, U.S. Pat. No. 4,270,946 or the like. As the most ordinary method for producing the above-mentioned compounds, there is known a method comprising producing a carboxylic acid, halogenating the carboxylic acid and then reacting the halogenated carboxylic acid with amine. In the above Japanese Patent Application Laid-open (KOKAI) No. 4-290805, it is described that pyridine carboxylic acid is produced by such an oxidation reaction of methyl pyridine as described in "J. Pharm. Belg." (1980), 35, 1, 5-11.
However, it has been difficult to produce the pyridine carboxylic acid having an oxidation-susceptible substituent group bonded to a pyridine ring thereof, such as an alkyl group, an amino group or a group having thiol ether bond, by the oxidation reaction such as oxidation of a methyl group with a high yield.
In addition, there is conventionally unknown any method of producing N-substituted pyridine thiocarboxamide without sulfidization of N-substituted pyridine carboxamide, until the process according to the present invention has been proposed herein by the present inventors.
The present invention has been attained in view of the above-mentioned problems. It is an object of the present invention to provide a industrially useful process for producing N-substituted pyridine carboxamide or thiocarboxamide, which can reduce limitations to production thereof.
As a result of the present inventors' earnest studies concerning a novel process for the production of N-substituted pyridine carboxamide or thiocarboxamide, it has been found that by reacting a pyridine metal compound and substituted isocyanate (or isothiocyanate) with each other, the aimed products, even N-substituted pyridine carboxamide having an oxidation-susceptible substituent group, can be produced with a high yield, and N-substituted pyridine thiocarboxamide can be produced with a high yield without sulfidization of N-substituted pyridine carboxamide. The present invention has been attained on the basis of the finding.